Growing plants in a green house has been a well known technology used for centuries. The key element of a green house is its covering which must be transparent or tranlucent but still be able to retain a significant portion of the heat generated by the sun or other means in the green house. Improved technology for the production of glass, especially economical production of large thin sheets has certainly advanced the use of green houses.
The advent of a thin plastic film has resulted in a widespread adoption of these films as a preferred covering for commercial green houses. Thin plastic films, which can be made in extremely large sheets and which can cover large square surface areas, are much lighter and much less expensive than glass. However, one of the deficiencies of thin plastic sheets are their thinness which results in a lack of heat retention capabilities which other alternatives, such as glass have. Also, due to exposure to the elements, in particular ultraviolet radiation, the plastic films generally have a relatively short life when used outside. Use of ultraviolet (UV) reflective or protective barriers has to some extend alleviated this problem.
A number of attempts have been made to improve the heat retention ability of thin plastic film. One widespread technique currently used by greenhouse owners is to place two sheets of thin plastic film over the framework of a green house and blow air in between them. The edges of the two sheets of plastic film are secured together at the appropriate places providing the sealed chamber necessary to contain and maintain inflation. However, the deficiency of this method is the requirement of the constant air pressure between the two sheets to maintain inflation and thus the space between the sheets which creates the insulating effect. If the seal happens to break at any point air pressure will fall and the inflation which maintained the separation of the sheets will be lost. Attempts have been made to solve this problem with more rigid plastic panels which have air spaces created between sheets of rigid polycarbonate plastic which make up the panel. However, this technology has its own problems and deficiencies, among them the need for more permanent structures to bear the weight of the panels